updated configure.ac to automatically check availability of a few headers required by crossedit
Basically, it tries to compile a test code having only includes of xaw, posix, etc. Should be
enough to prevent most crossedit compilation issue but not perfect. (Should check version of lib and
try a few methods on them). crossedit/ and test/unit/crossedit are skipped by make if test fail.

*/Makefile{in.am}: Fix plugin makefiles so that 'make distcheck' works. Using
relative path names for files to include in distribution does not work -
need to have a makefile in each directory.
configure{.ac}: Updated as result of new Makefiles.
MSW 2006-02-24

Version 2.0 of the Animator and Python plugins. Part of the transition to version 2.0 of the plugin interface.
An empty template for plugins writing as well as a library of common wrappers are also provided.
Gros - 18/10/2005